At the Weekly Standard, Jeffrey Anderson shows that, as with so many conflicting poll bottom lines this year, the disparity in Iowa seems mostly due to differences in the extent to which Democrats and Republicans are represented in the projected party turnout.

WeAskAmerica doesn’t report projected party turnout, but the other three polls do. The two that show Obama ahead (by 6 and 4 points, respectively) project, on average, 4.5 percent more Democrats voting than Republicans. Meanwhile, Rasmussen, which has Romney up by 1 point, projects a 4 point edge in turnout for Republicans.

It seems implausible to suppose that this year, compared to the Republicans, the Democrats will actually have a bigger slice of the Iowa turnout than they enjoyed four years ago. Yet this is what Gravis and Marist project.

Whether things have changed enough to give Republicans the 4 point turnout edge that Rasmussen projects is another question.

One way to think about that question is to compare Iowa party affiliation to national party affilation. In 2008, as noted above, Iowa’s party-affiliation split was 6 points to the “right” of the nation as a whole. If that variance holds, a 2 point Democratic affiliation edge nationwide would translate into the 4 point edge in Iowa that undergirds Rasmussen’s project of a 1 point Iowa victory for Romney. And Gallup shows Republicans with a 1 point edge nationally.

Anderson notes that Rasmussen actually shows Obama doing much better among independents in Iowa than Gravis does. So perhaps Rasmussen is finding Republicans where Gravis is finding independents. That would help explain why Rasmussen is projecting a 4 point Republican turnout edge, while Gravis projects a 6 point edge for the Dems.

So who’s ahead in Iowa? The answer may very well be: none of the above, right now.